1. Field of the Invention
The present invention relates to connecting devices of vehicle seats. More particularly, the present invention relates to connecting devices for rotatably connecting two components (e.g., seat backs and seat cushions) of vehicle seats. Further, the present invention relates to gears (gear assemblies) used in the connecting devices. More particularly, the present invention relates to gears (gear assemblies) that mesh with each other.
2. Description of Related Art
Generally, a vehicle seat includes a seat back and a seat cushion. The seat back and the seat cushion are rotatably connected via a seat reclining device for adjusting a tilt angle of the seat back. Such a seat reclining device is taught, for example, by Japanese Patent Number 4029847, which corresponds to U.S. Publication Number US 2007/0032332 A1.
The known seat reclining device includes an external gear wheel affixed to a seat cushion (a cushion frame) and an internal gear wheel affixed to a seat back (a back frame). The external gear wheel has teeth that are formed in a (toothed) outer circumferential surface thereof. Similarly, the internal gear wheel has teeth that are formed in a (toothed) inner circumferential surface thereof. The external and internal gear wheels mesh with each other. Further, the number of the teeth of the external gear wheel is set to be different from the number of the teeth of the internal gear wheel.
In the seat reclining device thus constructed, the external gear wheel is relatively moved along the toothed inner circumferential surface of the internal gear wheel while the external gear wheel meshes with the internal gear wheel. At this time, the external gear wheel can move along the toothed inner circumferential surface of the internal gear wheel while meshing points of the external and internal gear wheels are sequentially changed. As a result, the external and internal gear wheels are gradually rotated relative to each other due to a difference between the number of the teeth of the external gear wheel and the number of the teeth of the internal gear wheel, so that the seat back is rotated relative to the seat cushion. Thus, the tilt angle of the seat back can be adjusted.
Further, in the known seat reclining device, the external and internal gear wheels are respectively formed as trochoid curve gear wheels. That is, each of the external and internal gear wheels has a tooth profile that is defined by a trochoid curve. The trochoid curve gear wheels, when mesh with each other, can form an arcuate or curved meshing line (a line connecting a plurality of contacting points). Therefore, the external and internal gear wheels can have an increased meshing ratio. As a result, the trochoid curve gear wheels can produce an increased meshing force.